Device for testing the hardness of metals



Jan. 26, 1954 A. ERNST DEVICE FOR TESTING THE HARDNESS OF METALS FiledJuly 25, 1950 l" K ":4 I mars I g:

atented Jan. 26, 1954 STATES ATENT OFFICE DEVICE FOR TESTING THEHARDNESS F METALS Claims priority, application Great Britain July 27,1949 3 Claims.

This invention relates to devices for testing the hardness of metals, ofthe kind, of which an example is described in the specification of myBritish Patent No. 627,745, in which a plunger is pressed manuallyagainst the surface of the metal to be tested, and an indentorassociated with the plunger is subjected to a predetermined pressurewhich produces a degree of penetration of the metal depending on thehardness, so that the position of the indentor relative to the plungeris a measure of the said hardness, means being provided for indicatingsuch position on a scale.

The object of the present invention is to provide a device of the kindreferred to in which the reading obtained is substantially unaffected bythe degree of pressure applied by the operator.

According to the present invention, in a device of the kind referred tofor testing the hardness of metals resilient means are provided throughwhich the pressure is applied to the plunger, said resilient means beingarranged to transmit without yielding a maximum pressure only slightlygreater than the predetermined pressure applied to the indentor.

The resilient means preferably comprises a prestressed coil spring.

The invention is hereinafter described with reference to theaccompanying drawings, in which:

Figure 1 is a vertical section through one form of device according tothe invention;

Figure 2 is a partial vertical section taken at right angles to thatshown in Figure 1; and

Figure 3 is a plan view.

Referring to the drawings, the device comprises a circular base it withwhich is integrally formed an upstanding sleeve i I in which is slidablymounted a plunger !'2. The plunger carries at its upper end a headgenerally indicated at E3, and an indentor it having a point l5 at itslower end is mounted slidably in a co-axial bore in the plunger l2, theindentor I 4 being urged downwardly with respect to the plunger l2 by aspring it which exerts a predetermined load on the said indentor.Downward movement of the indentor is limited by an adjustable stop inthe form of a grub-screw 18 mounted in a block I 9 of hardened steel letinto the lower end of the plunger and held in position by a grub screw20, the stop so positioning the indentor that its point l5 projects asmall distance below the plunger.

The head it comprises a part 2| having a recess 22 on its underside, therecess being closed by a disc 23 which is screw threaded on its edge toengage a screw thread on the circumferential wall of the recess, and hasa screw-threaded cen tral aperture to receive the screw-threaded upperend of the plunger 12. A flexible diaphragm 24 is clamped betweenannular ribs 25 and 26 formed in the recess 22 and on the disc 23respectively, and constitutes a movable lower wall for a liquid chamber27 to which is connected a tube 23 of small bore, the tube, which is oftransparent material such as glass, being so shaped as to lie in anannular groove 29 extending around the upper surface of the head l3. Theliquid chamber is filled with liquid, which extends into the tube, theother end of the tube having a restricted opening to the atmosphere.

The upper end of the punch It bears against a rigid metal disc 30 whichis soldered to the underside of the diaphragm, and it will be seen thatrelative movement of the punch M and the plunger l2 will cause a changein volume of the liquid chamber 21, thus producing a movement of liquidin the tube which can be measured on a scale 3i engraved on theunderside of a cover 32 of transparent plastic moulding material clampedto the head by a central screw-cap 33.

A sleeve 34, internally screw-threaded at its upper end, is screwed atthat end on to the plunger, the sleeve 34 extending downwardly aroundthe sleeve H of the base, and having an external flange 35 at its lowerend to provide an abutment for the lower end of a coiled spring 35. Thespring 36 engages at its upper end with an internal flange 31 on thebody part 38 of a manual pressure member 39, the body part 38 being oftubular form and extending downwardly around the base it). The spring 35urges the body part 38 of the manual pressure member upwardly againstthe underside of the disc 23, and is compressed during assembly of thedevice to such a degree that it yields to permit the part 38 to moveaway from the disc 23 when a pressure slightly greater than that neededto compress the spring I6 is exerted on the manual pressure member.Downward movement of the manual pressure member is limited by anupwardly-projecting rim 40 on the base it, the arrangement being suchthat this rim 40 is engaged by the manual pressure member before thespring 36 is fully compressed.

The manual pressure member includes, in addition to the body part 38, apart 4| which is pivotally attached to the body part by means of setscrews 42 screwed into the part 38 and having non screw-threadedextensions 42a which enter holes in the body part 38, the pivot axis ofthe part 4| being perpendicular to, and intersecting by the spring [6,

the axis of the plunger [2. The part 4| has two opposite laterallyprojecting wings 43 the centre line of which is perpendicular to thepivot axis of the part.

A third spring 44 arranged between the base it and the body part 38 ofthe manual pressure member urges the manual pressure member and plungerupwardly with respect to the base, such upward movement being limited bya stop screw 45 mounted in the base and projecting into a slot 46 in theplunger.

A screw-threaded plug 41 mounted in the head l3 below the screw-cap 33provides a means for varying the volume of the liquid chamber 21 toadjust the zero reading of the device.

The base, plunger, head and sleeve of the device are conveniently madeof steel, whilst the parts of the manual pressure member may be of brassor other metal, or may be moulded in synthetic resinous mouldingproduct.

In use, the base of the device is placed on the surface of the materialthe hardness of which is to be determined and pressure is applied by theoperators hands to the wings 43 of the manual pressure member, thuspressing the plunger :2 down into contact with the surface of thematerial. The pressure exerted on the plunger is limited by the spring36. The indentor id, being urged downwardly relative to the plungerpenetrates the material to an extent dependent on the hardness of thelatter. The loading of the spring 46 is such that the degree ofpenetration of the indentor into the material is less than the initialprojection of the indentor beyond the end of the plunger, and theplunger !2 therefore moves downwardly relative to the indentor to makecontact with the surface of the material by a distance equal to thedifference between the initial projection of the indentor and thedistance of penetration. The volume of the liquid chamber 21 is thusdecreased by an amount dependent on the degree of penetration, and thecolumn of liquid in the tube 23 is increased in length, the increasebeing read: le on the scale, which is calibrated in accorda 3-3 with anydesired scale of hardness measurement.

The base it is provided with a diametral groove 48 on its underside tolocate the device on curved surfaces.

It will be understood that if the spring 35 were not included, theoperator would be dependent entirely on his own judgment for determiningwhat pressure was being exerted on the plunger, and he would not be surethat the plunger was in fact in contact with the material being tested,or whether he was exerting such a high pressure that the plunger itselfwas producing slight indentation of the material. With the arrangementaccording to the present invention the operator can safely exert themaximum pressure of which he is capable, the spring 36 yielding when thedesired pressure on the plunger is exceeded.

What I claim is:

1. A device for testing the hardness of metals comprising a plunger,means for applying manual pressure to said plunger to press one endthereof against a metal surface of which the hardness is to be tested,an indentor reciprocably mounted within said plunger, first resilientmeans interposed between said plunger and said indentor and urging saidindentor to a position in which it projects from the said end of theplunger, indicating means operated by relative movement of the indentorand plunger, and second resilient means interposed between the plungerand the manual pressure applying means, both said springs beingpreloaded, said second resilient means being preloaded in an amountsufiicient to transmit, without yielding, a maximum thrust slightlygreater than the load exerted on the indentor by the first resilientmeans.

2. A device for testing the hardness of metals comprising a plunger,means for applying manual pressure to said plunger to press one endthereof against a metal surface of which the hardness is to be tested,an indentor reciprocably mounted within said plunger, a first coiledspring interposed between said indentor and said plunger and urging saidindentor to a position in which it projects from the said end of theplunger, indicating means operated by relative movement of the indentorand plunger, and a second coiled spring interposed between the plungerand the manual pressure applying means, both said springs beingpreloaded, said second coiled spring being preloaded in an amountsufficient to transmit without yielding a maximum thrust slightlygreater than the load exerted on the indentor by the first resilientmeans.

3. A device for testing the hardness of metals comprising a base, aplunger slidably mounted in said base. an indentor slidably mounted insaid plunger, first spring means interposed between said plunger andsaid indentor and acting to urge said indentor downwardly with respectto said plunger, indicating means carried by said plunger and operatedby relative movement of the plunger and indentor, manual pressureapplying means including a sleeve surrounding said plunger, secondspring means interposed between said plunger and the manual pressureapplying means, both 1 said springs being preloaded, said second springmeans being preloaded in an amount sufficient to transmit withoutyielding a maximum thrust slightly greater than the load exerted on theindentor by the first spring means, and third spring means interposedbetween said base and said manual pressure applying means acting to liftsaid means and said plunger relative to said base.

ALFREDO ERNST.

References Cited in the file of this patent UNITED STATES PATENTS

